Three-dimensional unoccupied band structure of graphite: Very-low-energy electron diffraction and band calculations

The unoccupied band structure of single-crystal graphite above the vacuum level is studied by very-low-energy electron diffraction. The position and dispersion of the three-dimensional bands coupling to vacuum, including the so-called interlayer state, are determined. The three-dimensional character prevails in the unoccupied bands, but quasi-two-dimensionality of this layered material results in their strongly non-free-electron dispersion. By comparison to a state-of-art density-functional and a many-body band calculation we identify self-energy corrections.